A typical battery has two terminals. One terminal is marked (+), or positive, and the other is marked (−), or negative. In normal flashlight batteries, such as conventional AA, C or D cell batteries, the terminals are located at the opposed ends of the battery. To harness the electric charge produced by a battery, the battery must be connected to a load, such as a light bulb, a motor, or an electrical circuit.
The internal workings of a battery are housed within a metal or plastic case. Inside this case are a cathode, which connects to the positive terminal, and a corresponding anode, which connects to the negative terminal. These components, which are electrodes, occupy most of the space in a battery and are the place where the chemical reactions occur to produce electricity. An insulator or separator creates a barrier between the cathode and anode isolating the cathode from the anode preventing the electrodes from touching while allowing electrical charge to flow freely between them. The medium that allows the electric charge to flow between the cathode and anode is known as the electrolyte. A collector conducts the charge to the outside of the battery and through the applied load.
When a load completes the circuit between the positive and negative terminals, the battery produces electricity through a series of electromagnetic reactions between the anode, the cathode, and the electrolyte. The anode experiences an oxidation in which two or more ions from the electrolyte combine with the anode, producing a compound and releasing one or more electrons. At the same time, the cathode goes through a reduction reaction, in which the cathode substance, ions, and free electrons also combine to form compounds. The reaction in the anode creates electrons, the reaction in the cathode absorbs them, and the net product is electricity. The battery will continue to produce electricity until one or both of the electrodes run out of the substance necessary for the reactions to occur. Modern batteries use a variety of chemicals to power their reactions. Common battery chemistries include zinc-carbon batteries, alkaline batteries, lithium-ion batteries, and lead-acid batteries.
The zinc-carbon chemistry of zinc-carbon batteries is common in many inexpensive AAA, AA, C, and D dry cell batteries, in which the anode is zinc, the cathode is manganese dioxide, and the electrolyte is ammonium chloride or zinc chloride. The chemistry of alkaline batteries is also common in AA, C, and D dry cell batteries. In alkaline batteries, the cathode is composed of a manganese dioxide mixture, the anode is a zinc powder, and the electrolyte is potassium hydroxide, which is an alkaline substance. The lithium chemistry of lithium-ion batteries is often used in high-performance devices, such as cell phones, digital cameras, and electric cars. Lithium-ion batteries are rechargeable, and a variety of substances are used in lithium batteries, and a common combination is a lithium cobalt oxide cathode and a corresponding carbon anode. Lead-acid batteries are also rechargeable, and the corresponding chemistry, which is used in conventional car batteries, includes lead dioxide and metallic lead for the electrodes, and a sulfuric acid solution for the electrolyte. The most common form of rechargeable battery is the lithium-ion battery.
With the rise of portable electronic devices, such as laptops, cell phones, flashlights, cordless power tools, and the like, the need for rechargeable batteries has grown substantially in recent years. Many portable electronic devices that use rechargeable batteries incorporate one contact region for an operating circuit for operating the load, and a second contact point for a charging circuit used to recharge the battery. The operating circuit operates separately from the charging circuit. This is normally achieved by using either a battery cradle that contains the necessary circuits, or an inner barrel inside the body of the electronic device to carry the extra current. Although both methods are effective, they add extra weight and increased cost in the product of the electronic devices and in some instances make it inconvenient and cumbersome to remove or replace a battery as may be necessary from time-to-time. Given these and other deficiencies in the art of batteries, the need for continued improvement in the field is evident.